The proper chromosome transmission in mitosis is facilitated by numerous cellular factors. Particularly, chromosome proteins are actively engaged in mitotic segregation of chromosomal material. The newly discovered family of chromosomal proteins, the SMC family, represents an important subset of these polypeptides. The SMC-proteins are present in most of the cellular organisms. Their importance is especially profound in the process of chromosome condensation during mitotic prophase. They also are indispensable for the disjoining of sister chromatids during an anaphase. Thus this family is one of the central players in the mitotic chromosome segregation. The goal of the ongoing studies is to elucidate the molecular mechanics behind the activity of these proteins in mitosis. This work follows four major directions. First, structure-function analysis of the SMC molecules, beginning with assigning a biochemical activity or a cellular function to the putative domains of the given SMC-protein. These studies include mutational analysis of four SMC genes in bakers yeast (SMC1, SMC2, SMC3, SMC4) and development of the system for allele replacement of mouse smcA, smcB and smcD genes in cell culture. Second, cell cycle specific distribution and regulation of the SMC-proteins is being assessed through the studies of their subcellular localization. For that purpose the polyclonal antibodies are being generated against all yeast SMC proteins, and the monoclonal antibodies against human SmcA and SmcB are at the stage of development. Third, the pilot experiments have been done, aimed at the development of the in-vitro assay for chromosome condensation employing controlled number of purified components. This direction of studies is necessary to assess the actual molecular function of the SMC-proteins. Fourth, we conduct a biochemical and genetic search for the proteins interacting with the SMC proteins, both in yeast and mammalian cells. Three proteins interacting with the SMC function in yeast has already been identified.